CAUSES OF DIAGONAL STRATIFICATION. 
43 
due to original deposition? We must suppose that at the 
bottom of the sea, as well as in the beds of rivers, the mo¬ 
tions of waves, currents, and eddies often cause mud, sand, 
and gravel to be thrown down in heaps on particular spots, 
instead of being spread out uniformly over a wide area. 
Sometimes, when banks are thus formed, currents may cut 
passages through them, just as a river forms its bed. Sup¬ 
pose the bank A (Fig. 4) to be thus formed with a steep 
sloping side, and, the water being in a tranquil state, the lay¬ 
er of sediment No. 1 is thrown down upon it, conforming 
nearly to its surface. Afterwards the other layers, 2, 3, 4, 
may be deposited in succession, so that the bank B C D is, 
formed. If the current then increases in velocity, it may cut 
away the upper portion of this mass down to the dotted line 
6, and deposit the materials thus removed farther on, so as to 
form the layers 5, 6, 7, 8. We have now the bank B C D E 
(Fig. 5), of which the surface is almost level, and on which 
Fig. 5. 
the nearly horizontal layers, 9,10,11, may then accumulate. 
It was shown in Fig. 3 that the diagonal layers of successive 
strata may sometimes have an opposite slope. This is well 
seen in some cliifs of loose Fig. 6. 
sand on the Suffolk coast. A - — — 
portion of one of these is rep¬ 
resented in Fig. 6, where the 
layers, of which there are 
about six in the thickness 
of an inch, are composed of 
quartzose grains. This ar¬ 
rangement may have been Cliff between Mismer and Dunwich. 
due to the altered direction of the tides and currents in the 
same place. 
